Wilkins ice shelf collapse

Since people are wanting to talk about the latest events on the Antarctic Peninsula, this is a post for that discussion.

The imagery from ESA (animation here) tells the recent story quite clearly – the last sliver of ice between the main Wilkins ice shelf and Charcot Island is currently collapsing in a very interesting way (from a materials science point of view). For some of the history of the collapse, see our previous post. This is the tenth major ice shelf to collapse in recent times.

Maybe we can get some updates and discussion of potential implications from the people working on this in the comments….?

At the end of one of the nightly news shows last night (either ABC or CBS – not sure which channel I was on), the announcer covered this story and followed it up by saying that temperatures in the Antarctic had risen by 4 degrees. Is that correct? I thought parts of the continent had risen, other parts cooled, and on average the change (in Antarctica) was essentially within the noise. Thanks in advance.

[Response: Long term trends are positive over the whole continent, but much smaller than 4 deg. Almost certainly the announcer was referring to the Antarctic Peninsula warming which is where the Wilkins ice shelf actually is (and I’m going to guess F rather than C). – gavin]

How far out of the bounds of normal climate variability is this event? It seems to me as a non-scientist that ‘normal climate variability’ is more a function of ‘speed of change’ rather than ‘events differing from the immediate past’. Sir Nicholas Stern said that the Earth has seen temperatures 5 degress C above pre-industrial. So I don’t see that mere temperature increases above 2 degrees C that scientists now say we need to stay below is the real issue. But how quickly we are getting there, along with the chemical blanket of GHG that might take temperatures beyond anything the Earth has EVER seen.

[Response: “Natural variability” encompasses everything from Snowball Earth to the extreme mid-Cretaceous hothouse. So nothing is going to happen that is completely unprecedented over Earth history – but if that was your benchmark, you would consider climate change nothing to worry about until sea level was 100 meters lower or higher than today. Possibly a little late to address it… As for Wilkins, the estimates are that there has been an ice shelf there for about 10,000 years. I think that’s pretty significant, but YMMV. – gavin]

Quick question: how significant is it that there have been a series of collapses like the ten mentioned in the story. Is this noticeably different in pace and scope from the recent (last few hundred years) pattern?
I partly ask this to help educate people who I direct to your site. My own educated guess is that this pace is accelerating. Am I right?
Thanks.

Mercer, Nature, 1978, v271 pp.321-325
“One warning sign that a dangerous warming is beginning in Antarctica, will be a breakup of ice shelves in the Antarctic Peninsula just south of the recent January 0C isotherm; the ice shelf in the Prince Gustav Channel on the east side of the peninsula, and the Wordie Ice Shelf; the ice shelf in George VI Sound, and the ice shelf in Wilkins Sound on the west side.”

But should the “pace” remain consistent? Not hardly.
So while it may be convenient to assume this event is somehow attributed to AGW that remains to be merely an assumption without enough science to signal causation or correlation.

The ice shelf collapse is a local event, I assume, as are some of the local “cold” events occurring in the other hemisphere (record snows, this spring’s Arctic T’s, etc.). RC will be and has been very careful to note that local events are “weather” and to be ignored in the larger scheme of things. I can anticipate some criticism being levied (it’s probably already out there) along the lines, “As long as the local event is hot, it’s AGW, but if it’s cold then it’s either a natural effect or a temporary anomaly,” something along those lines. What is the distinction, and, please, this is a straight-up question, not a rhetorical one.

[Response: Ice sheets/shelves are great integrators of changes over a long time scale (whereas a weather event is not). And it is not an isolated event – ice shelves up the Peninsula have been collapsing, as have those in the high Arctic (e.g. Wordie). And it’s hardly a counter-intuitive result…. Having said that, there are a number of dynamical factors which make the Peninsula region a little special (the increase in the SAM which is impacting local sea ice cover and the winds for instance) – but they are likely anthropogenic too. – gavin]

PBS NOW is doing a series on the effects of Global Warming that is more than convincing.

On April 17 NOW will air a special hour long edition on how mountain ice is receding. That will make for tough going in late summer when glacier fed rivers run dry. Pack the kids up soon to visit Glacier National Park—the prediction is that its ice will be gone by 2021—9 years sooner than predictions 5 years ago. About the time when the renewable portfolio standards in states other than Montana are saying we should produce 20% of our electricity with renewables—too late to save Glacier. You can view a preview athttp://www.pbs.org/now/on-thin-ice-preview.html

The Wilken’s ice shelf is about 16,000 km^2 compared to a total over 1,500,000 km^2 of ice shelves in Antarctica. That makes it roughly 1% of the total and these types of break ups do not happen every year. Obviously, it will be a while before there is a substantial reduction in the amount of Antarctic ice shelves.

When ice shelves float into the ocean, they eventually break up into smaller pieces. Initially several hundred meters thick, they become thinner and cover larger areas. So, is the breakup of ice shelves a significant contributor to the extent of sea ice?
Notice, that in contrast, the Arctic has relatively few ice shelves. Over 90% of those that were in existence a hundred years ago have long since broken up. Consequently, the breakup of ice shelves can no longer be a significant contributor to sea ice in the Arctic.
Are there any papers published in peer reviewed science journals that offer up an explanation for the trend in Antarctic sea ice?

In response to wmanny at 10:32 AM: The reason why this collapse is an important indicator of warming and not merely a local event is that for an ice shelf to collapse, it takes a consecutive series of warm years to progressively weaken the shelf. It does not merely happen overnight. If these shelves stood for at least 10000 years, and are now collectively collapsing in a geological blink of an eye, then this is a strong indication of a warming trend. This trend is even more strongly demonstrated if we take into account all of the other shelf collapses, both in the Southern and Northern Hemispheres, as well as the strong reduction of summer Arctic Sea ice.

I wanted to ask you a question based on your own…if this is not attributable to AGW, especially considering that it is now the tenth ice shelf to ‘disembark’, to what, exactly, would you attribute Wilkins? You imply in your remark that there are other means for such an event to happen. If your skepticism is to have legs, then give me a plausible counter-explanation. You used emotionally loaded terms like ‘not hardly’ and ‘convenient’ in your post, which seemed to me to signal an inflexible, pre-existing opinion. Prove me wrong.

steve missal (12),
it could be ice-eating fish nibbling away at the bottom of the shelves, or hank’s “global expansion” theory, whereby the glaciers and ice sheets are being “lifted” above the water thus causing faster glacier flow toward the water and collapsing of the rising ice sheets. it could be.

Many thanks for starting this thread (I wasn’t nagging earlier ..!). I have had a look at the ESA animation, and although it is rather bitty (swath coverage etc.), it’s certainly very striking how the ice margin on the lower main spur of the ice bridge develops an irregular, almost saw-toothed boundary, whilst the spur itself becomes densely cracked and creviced. At the same time, the crack running at about 2 o’clock from Latady Island seems to be getting more definite (deeper? wider?); not clear whether the latter is an image processing effect or some other artefact, though. If the ice boundary along that bit of the shelf develops a similar, saw-tooth pattern, that could well indicate major changes to follow. It’ll be interesting to see if the encroaching Winter down there can stall further changes until next season: it could be a close run thing.

Regarding isostatic effects, I was wondering whether sudden de-shelving at the margin can lead to development of a positive feedback between ice slope and ice velocity. It might seem a bit counter-intuitive, but if the coastal ice (not really coastal, but I can’t think of a better word) melts, this area should start to rise from the effect of the unloading (i.e. where this ice had hitherto been resting on the sea floor). On the other hand, areas still well iced over will also start to sink a bit in compensation, through the leveraging the rebound generates. Thus, where the ice is still resting on the sea bed, it depresses slowly into deeper water, increasing the upthrust and reducing friction along the bed plane. In absolute terms, the movements are fairly small to begin with, but where the resistance to sliding is close to a threshold, a small change can have a big effect. Be interesting to hear from anyone who has looked into this.

A lay question. As I understand the position, precipitation in Antarctica occurs mainly as snow. As the snow builds up, it compresses to ice, and gravity causes it to flow (very slowly?) towards the coast, and then on to the sea as iceshelves. So we are perhaps looking at a dynamic system, with snow being added to the system, compressing to ice and flowing towards the ocean, pushing out onto the sea, and eventually breaking up.

Is this accurate? Do we have a good understanding of the process? How can we tell whether the breakup of iceshelves is just part of a natural ongoing process as described above, or is it to do with warmer ocean currents affecting the coast, or is it to do with AGW?

Seriously, make some effort to look these things up and think them through, you’ll find a great many papers, none of us have time to read them for you, but if you read them and then ask questions about them someone who actually knows the area may reply.

I’m asking these questions to help me explain all this to average citizens as part of my volunteer organizer work with 1Sky.org. So the ‘2 degrees above C’ ceiling proposed by scientists (preferably below according to James Hansen and Dr. Ware from Pottsdam) has more to do with ‘climate range conducive to human existence w/o massive thirst and starvation given our current population and ability to feed it, and to prevent extreme weather events/temperatures harmful to humans like above-average summer temperatures for longer periods of times, than what has happened before in the history of the Earth?

In my own words, Zhang’s paper shows how a stagination of the oceans around the continent could lead to less heat transport from lower in the ocean and a greater volumn of sea ice.

Also, it may be due to simply lower salinity of the water, thereby greater formation of ice despite rising temperatures.

However, along my original line of thought. The Wilkens shelf is probably about 300 meters thick. Sea ice around the continent averages about 1.5 meters. So, the 15,000 km^2 shelf will eventually break up into about 3,000,000 km^2 of sea ice. That is a lot of sea ice and of course it will also lead to lower salinity and reduced salt rejection, enhanced thermalhaline stratification and weakened convective overturning.

Andrew, the first point to make is that the trend in Antarctic sea ice is not statistically significant. If you look at the plots and compare them with those for the Arctic you can sea that there is much more year-to-year variation in Antarctic sea ice.

This isn’t surprising when you consider the geography of Antarctic sea-ice surrounding a continent, whereas in the Arctic it is the other way around – consequently sea-ice in Antarctica exists at lower latitudes and is more prone to being blown about and compacted, or not, by the winds.

I’ve also read that the ozone hole has had an effect on the Antarctic circulation, which is why Antarctica is the part of the globe that has warmed least [or not at all]. If the ozone hole recovers as expected, one would consequently expect to see particularly rapid Antarctic warming in the 21st century.

[Response: It’s quite useful to look at the trends as a function of space. You will easily see that sea ice is way down on the west side of the peninsula in the region of Wilkins during March (sea ice minimum conditions). – gavin]

First you need to understand how much of current change is pushed by fossil fuel use, how much “A” in the current “GW” or you can’t understand the question you’re asking. That’s in Spencer Weart’s book, first link under Science.

Then you need to understand rate of change — how fast is the change now compared to previous warming events.

And you need to understand what sources you can rely on to tell you the truth about the research.

Try your question first in Google Scholar, then compare what you get in ordinary Google. You’ll find the science papers documenting the research answer your questions. And you’ll find the difference with ordinary Google is a lot of the old familiar sources teaching uncertainty and doubt.

“How can we tell whether the breakup of iceshelves is just part of a natural ongoing process…”

The Wilkins Ice Shelf was around for ten millennia. So this breakup was not an ‘ongoing’ process.

“is it to do with warmer ocean currents affecting the coast”

Yes.

“To the extent that the ocean warms, and that warm water reaches beneath the ice shelf, it’s very likely to increase the rate of melting near the grounding line in particular. That could have a number of effects,” Jacobs said.

From their observations, the researchers estimate that for each rise in ocean temperature of 0.1 degree Celsius (0.2 degree Fahrenheit), the melting rate near the grounding line should increase by 1 meter (39.37 inches) per year.

Scientists have already detected a 0.2 degree C (0.36 degree F) increase in recent decades. This rise is large enough to explain the rapid thinning observed for ice shelves in some parts of Antarctica, and the acceleration of the glaciers that nourish them, according to the researchers. ”

The Climate Progress site has what looks to be an informative article, with a number of links to related scientific papers and mainstream news reports:

Q: How much can West Antarctica plausibly contribute to sea level rise by 2100?

A: 3 to 5 feet — contributing to an increasingly likely total sea level rise of more than 5 feet by 2100, a rise that will be all but impossible to stop if we don’t sharply reverse CO2 emissions trends within a decade or so.

The public focus has been on when will the bridge collapse. However, given the clearly untenable nature of the narrow connection ot Charcot Island, the more important question is how far back into the Wilkins ice Shelf does instability exist. Humbert and Braun have noted for this ice shelf and Scambos and Shepard for Larsen the importance of rifting which show pre-conditioned weaknesses. It is evident that south and east of the precarious bridge an extensive rift system has been expanding. A comparison of the November 2008 image which dates the time of rift formation below the narrow and unsound bridge. http://www.esa.int/images/asar200904022_H.jpg
Humbert and Braun have annotated rift development dates.
Compare this to the April 2, 2009 image. Focus on the rift just above the word Wilkins in this image. This rift has become even longer and wider. The ice shelf beyond this rift is effectively unstable.

Re comment #2:FM says:
“the announcer covered this story and followed it up by saying that temperatures in the Antarctic had risen by 4 degrees. Is that correct?”

This can’t be in degrees C. In an article in the May 1,2008(p.13) issue of “Nature”, Tim Naish,a project leader at the Institute of Geological and Nuclear Sciences in Lower Hutt, New Zealand,says “That(the rapid and substantial melting of the West Antarctic ice Sheet and the Ross Ice Shelf, raising global sea levels by up to ten metres) happened at a time when it was three to four degrees(C) warmer than today,owing to atmospheric carbon dioxide concentrations, which we will very likely reach again soon,”…..

The article goes on to state that David Pollard, an ice sheet modeler at Pennsylvania State Univ.,presented simulations that western Antarctica can lose almost all of its ice at temperatures just three to five degrees higher than todays.

7. Gavin, thanks, and some logical questions arise: do climate theorists/modelers believe SAM or AGW is the greater factor here? How well understood, for example, does the IPCC believe SAM to be? (I could find no reference to it in AR4, Sec. 4, – though NAM is mentioned – but I’m probably looking in the wrong place.)

If I recall correctly (low odds) SAM is a relatively recent observed phenomenon (40’s?, 50’s?) whose forcings are theorized to be aerosol/ozone based? As you can tell, I’m out of my depth and curious.

I wonder if anyone has looked into the the effects of warming caused by the asphalt and black roofing shingles used on houses. In the summer on a roof covered in black shingles, the temperature in NC can be 95f and on the roof it is roughly 105-130f depending on cloud coverage and wind.

You’ve answered a question with a question. My query was pretty straightforward. You expressed doubt, so I would like to know what you might suggest as an alternative. That’s all. There are numerous supporting studies viz AGW and Antarctica that can be found on this site and elsewhere…I just wanted to know how these iceshelf collapses might occur other than AGW. Do you have a theory, or could you summarize someone else’s theory that that is contrary to AGW concerning the Wilkins topic?

Thanks, and glad my memory wasn’t utter crap. One could interpret the 10.17 discussion as implying the Wilkins collapse has more to do, then, with 20th-century ozone depletion than it does AGW trends. That appears to be the IPPC read at any rate.

The news pictures showed a “road” cut along the ice bridge to Charcot Island. Fracture Mechanics would treat this as a “notch” which, according to Griffiths theory, would enormously weaken the structure. Have we just seen man-made destruction of a different kind from melting?

re: #38 Matt T
re: roofs:
Yes, people have looked into it, which is why Google: california cool roofs
will show you many hits.

However, while such is very important in some areas, where it can substantially reduce air-conditioning load and bad interactions with local pollution, painting Antarctic roofs white is not likely to offer major benefits.

Actually, Hank’s expansion might not be quite as far out as it might seem at first. If as the GRACE satellite package indicates, the Antarctic ice mass is being reduced, there could be a portion of uplift (rebound) near the coastal regions that could be contributing to the fracturing of the sea borne ice floes. Combined with the 1990s higher SSTs over topping the regional sea currents suggests both events could be part of the driver of the recent events on the Western Peninsula.

This of course would return us to a discussion of the amount of heat energy content of the Sea Surface and the causes. (For this we will have to defer to the experts.) However, if as has been indicated there is some continental warming in association with an increase in solar insolation that there is sufficient drivers to increase peripheral seasonal melt and move the melt perimeter closer to the pole.

(Note: The reduced land ice mass could also be playing a part in the rapidity of the change. It might even help suggest why the land ice appeared to be slowing in 2005/06. (If the slope is reduced then the slide towards the sea could slow and not have anything to do with “cooling” of the region or changes in precipitation.)

The end result would likely reflect Hank’s theory that there could be an “expansion” of sorts… As always folks I enjoy reviewing the banter. (BTW, Dr. Schmidt, I am pleased to see that counter opinions are getting a little more play.}

You folks know what the problem here is don’t you?
Too much interpreating, correcting and estimating and not enough accurate, calibrated measuring. And way too much pretending they are one in the same.

The same problem exists with other surface temperatures.
The inability to make reliable measurements over time diminishes the ability to gather accurate observations.

“We provide estimates of the warming of the world ocean for 1955-2008 based on historical data not previously available, additional modern data, correcting for instrumental biases of bathythermograph data, and correcting or excluding some Argo float data. The strong interdecadal variability of global ocean heat content reported previously by us is reduced in magnitude but the linear trend in ocean heat content remain similar to our earlier estimate.”

[Response: Did you read that reference? Did you notice that the long term trends in ocean heat content are all up? Did you notice that this was an independent analysis from Willis? or Domingues et al? Perhaps you would prefer that problems not be addressed? Or that unless everything was perfect ahead of time we can’t use it? – gavin]

These collapses are like canary’s in coal mines.If we don’t mitigate our burning of fossil fuels, there’s a possibility of very serious melting in the Antarctic with equally serious consequences.

If the rate of increase of CO2 into the atmosphere increases even to 1% of present value to about 4ppm per annum, how long would it take to double present values of about 390 ppm?
The calculation is straightforward. If a quantity increases by some fraction,f, of itself per unit time, in a small time interval dt ,the increment of the quantity dQ= fxQxdt or dQ/dt=fQ. The solution is given by Q(t)=Qoe^ft=Qox2^t/T where T is the doubling time and Qo is the present of Q. T=ln2/f. The percentage increase per annum is p=100f. Then T=100ln2/p ~ 70/p, in years. Then if the amount of atmospheric CO2 were to increase by 1% per year, it wil double in 70 years! That’s well within the lifetime of most of today teenagers! We really have to change our ways. Business as usual is not an option.

Also,who says the oceans are cooling?! Where do these people get their information from, K-Mart?

I guess I won’t be getting that optional theory after all. Perhaps I’ll be surprised, though. I’d still like to hear an actual theory from Dawn or any other skeptic. Something other than armchair stuff. I doubt sincerely that there is anything substantive that would fill the bill, but now is the opportunity to have at it and show me I’m wrong..
I’m pretty sure that Dawn or whomever else is a doubter will read this. This is it. Your golden opportunity. Really, I’m not being rude. Just direct. Give it a go and let’s take a look at some data substantiated alternative reason that might explain these types of events.